The present invention relates to a method for fabrication of industrial parts having high-aspect-ratio through-hole sections at high density, and, more specifically, when using a soft material which is deformed by handling after blanking, to a method for fabrication of industrial parts by which many high-aspect-ratio through-hole sections are formed into industrial parts with a predetermined thickness, with a similar high accuracy to that of hole sections drilled in a thin sheet material.
Reduction in cost, weight, and size has been commonly required in all industrial products, and, especially in industrial products equipped with many electrical circuits, a small size has been necessary for additional value to cause remarkable developments in packaging technologies for these circuits. Among these developments, small through-hole sections of the order of xcexcm have been required to be fabricated with good accuracy for wiring boards having electronic components mounted thereon so as to more densely integrate electronic circuits, while considering cooling effects, and to secure high reliability. Moreover, technologies to accurately drill small through-hole sections in industrial parts have been indispensable, for example, holes smaller than those of wiring boards, have been required to be drilled with very high accuracy for ink ejecting sections of inkjet printers.
Recently, there have been much more densely integrated electronic circuits, and it has been necessary to drill a larger number of small holes in a predetermined area of material substrates. Then, it has been necessary for the through-hole sections to be smaller and deeper in the hole dimension, in other words, for the diameter to be smaller and the axial length (depth) of the above through-hole sections to be longer. That is, it has been necessary for those aspect ratios to be higher. Therefore, it has been required to form the through-hole sections with high accuracy. Generally, the aspect ratio denotes the ratio of the diameter to the axial length of the hole when the cross section of the hole is a circle, and that of the shortest distance between mutually opposing edges of the hole to the axial length when not a circle. Here, the shortest distance between the mutually opposing edges of the hole is the shortest one S in FIGS. 5(a) and 5(b). That is, a high-aspect-ratio through-hole section means a long and narrow hole with a long axial length compared with the diameter or the shortest distance of the hole.
Hole-drilling with a blanking die may be listed as one conventional method for drilling a large number of small holes in such a sheet material. The above drilling is a method for making industrial parts by performing, at one time, blanking of a sheet material with a predetermined thickness using a punch and a die. In the above method, there has been a problem of poor accuracy as a thick sheet material is treated as a blanking object from the beginning, requiring a large clearance between the punch and the die. Moreover, a shearing force larger than that of a thin sheet material is applied during blanking, and a large number of holes are required, especially for the die, when the through-hole sections are formed with a high density. Therefore, the strength of the die may not withstand the above large shearing force, deformation may be caused due to shortage of the rigidity, and, furthermore, the problem of damage may also occur.
FIG. 3 shows a drilling state of a through-hole section with a blanking die. As shown in FIG. 3(a), cracks 15 are caused from each edge 14 of a punch 10 and a die 12 during blanking, when the punch 10 performs blanking of a sheet material 13 put on the die 12 after provision of a clearance 16 as a space between the punch 10 and the die 12. That is, the cracks 15 are generated in the vicinity of the clearance 16, and the accuracy of the hole varies within the range of the clearance 16. Thereby, according to the method for drilling of through-hole sections with the blanking die, the cross section of the through-hole sections of a sheet material after blanking is generally tapered in the blanking direction, as shown in FIG. 3(b).
The clearance 16 for the blanking die is required to be larger for a thicker sheet material, for example, 4-12% of the sheet thickness for thin sheets, and 18-26% of the sheet thickness for thick sheets, according to xe2x80x9cBASIC MACHINING (I)xe2x80x9d, published by THE NIKKAN KOGYO SHIMBUN LTD. That is, the accuracy of holes is reduced for a thick sheet material, as described above. Therefore, the above methods are not suitable for high-density drilling of high-aspect-ratio, small through-hole sections, as the sizes of the diameters at the exit side in the blanking direction are uneven.
As an improved method for hole drilling with the above blanking die, there has been a method for obtaining industrial parts with a predetermined thickness, by which, after the thin sheet materials undergo blanking, the thin sheet materials are transferred and laminated. In the above method, since the sheet thickness of the material for blanking at one time is thin, resulting in superior accuracy of the holes for each sheet of sheet material in each blanking and reduced shearing force caused by the punch and the die, holes may be drilled very densely. However, there are problems of low production efficiency and high cost, as jigs for transferring the sheet materials and space for lamination are required, and there are an increased number of machining steps. Moreover, since guide pins are needed for precise lamination, waste is also caused by drilling holes other than the necessary through-hole sections in the industrial parts. Furthermore, when using a soft material which can be deformed after blanking, and when the industrial parts are laminated to a predetermined thickness, gaps occur between holes after transfer and lamination and the problem of reduced accuracy of the holes occurs. Therefore, the above method is not suitable for very dense drilling of high-aspect-ratio, small through-hole sections.
As another conventional method, there is a method for hole drilling with a laser beam, not using the blanking die. It is machining with a laser beam, that is, a machining method in which a work material is exposed to the laser beam after the above beam is focussed with a lens. According to the above machining with the laser beam, there is a fundamental problem of poor accuracy in the case of the high-aspect-ratio through-hole sections, as the through-hole sections are tapered in the propagating direction of the laser beam due to the laser beam focussing method.
FIG. 4 shows a drilling state of a through-hole section formed by laser beam machining. As shown in FIG. 4(a), in a laser machining apparatus, a parallel beam light 17 passes through a condensing lens 18 and is focussed for machining at position of a focal distance 20. A greater distance from the focus causes the laser beam width 19 to become broader, that is, the diameter of the machined hole becomes larger. Thereby, in the case of a larger thickness of the sheet material, while the hole at the exit side in the propagating direction of the laser beam is being drilled, a hole with a larger diameter is drilled at the entrance side in the propagating direction of a laser beam. As a result, a tapered through-hole section will be formed, as shown in FIG. 4(b).
Moreover, as thermal energy is used for the laser beam machining, a sheet material to be machined is deformed by the effect of heat, and an altered layer is formed. Thereby, another problem of uneven hole diameters also occurs. Even in the above problem, a larger thickness of the sheet material causes a lower accuracy of the holes, as the sheet material with the larger thickness requires a larger amount of laser beam energy, that is, a larger amount of thermal energy. Therefore, it is also difficult to say that the above laser beam machining is suitable as a method for high- density drilling of high-aspect-ratio through-hole sections.
As described above, there have been many developments in higher density mounting technology for industrial fields, especially for electronic components, and, in industrial parts for which fine through-hole sections are required to be drilled at high density, methods for making high-aspect-ratio through-hole sections with no damage, more safely and with higher accuracy have been required, even when using a soft material having a dimension or a shape in which deformation may be caused by handling after hole drilling. However, suitable methods have not been proposed.
The present invention has been made, considering the above problems, and the object is to solve the problems in conventional technologies, and, to contribute to increased density packaging of industrial parts, especially, of electronic equipment, by provision of industrial parts having a predetermined thickness and a plurality of high-aspect-ratio, small through-hole sections, based on a configuration where, even when using soft material which can be deformed, there may be drilled fine through-hole sections with a narrow diameter, for example, 100 xcexcm or less, and with an axial length whose ratio with respect to the diameter is larger than a predetermined ratio; and the above drilling is performed with similar accuracy to that of through-hole sections drilled in one sheet of thin sheet material, and approximately in a cylindrical shape which are formed in a straight line.
The inventors of the present invention have examined various kinds of methods and fabrication steps for hole-drilling of a sheet material with a blanking die, and found that the following fabrication method achieves the above purpose: in a die blanking method for drilling a hole section in a sheet material, using a punch and a die, the above material is lifted in tight contact with a stripper under a state where the punch is not pulled out from the hole section, after drilling of the hole section in the sheet of sheet material with the punch; the punch lifted from the die is returned so as to be slightly drawn in from a bottom section of the hole section; similarly, the subsequent material is lifted in tight contact with the lower section of the previous sheet material, while being laminated on each other, under a state where the punch is not pulled out from the hole section, after drilling of the hole section with the punch; the punch lifted from the die is returned so as to be slightly drawn in from the bottom section of the hole section; and the above steps are repeated to laminate a plurality of sheets of sheet material with drilled holes in a device with the punch and the die.
That is, the present invention provides a fabrication method of an industrial part having high-aspect-ratio through-hole sections, using a punch and a die, including: a first step of drilling a first hole section in a first sheet of sheet material with the punch; a second step of lifting the above first sheet in tight contact with a stripper; a third step of lifting a tip section of the punch so as to be slightly drawn in from a bottom section of the lifted first sheet of sheet material; a fourth step of drilling a second hole section in a second sheet of sheet material with the punch; a fifth step of lifting the above second sheet in tight contact with the above first sheet; and a sixth step of lifting the tip section of the punch so as to be slightly drawn in from the bottom section of the lifted second sheet of sheet material; and, characterized in that the above fourth to sixth steps are repeated for bonding and lamination of a plurality of sheets of sheet material.
In the present invention, the accuracy of the above through-hole sections which are drilled in the above industrial part may be arranged to be similar to that of hole sections drilled in the above one sheet of sheet material.
Moreover, in the present invention, it may be possible to form high-aspect-ratio through-hole sections, that is, the ratio of the diameters, or the shortest distances from one edge to the opposing edge of the above through-hole sections to the axial lengths, approximately 1:1-1:7, and also to form through-hole sections with the ratio of the distance between the through-hole sections adjacent to each other to the axial length of the above corresponding sections approximately, 1:1-1:7. Moreover, it may be possible to form high-aspect-ratio through-hole sections, where the diameter of the above sections is 100 xcexcm or less; and also to form high-aspect-ratio through-hole sections, where the distance between through-hole sections adjacent to each other is 100 xcexcm or less.
In the present invention, sheets of sheet material to be laminated may be bonded to each other by using the above sheet material with a bonding agent previously applied thereto, or by inserting a bonding sheet between the sheets of sheet material. Furthermore, each sheet material may be laminated in tight contact with each other, using vacuum suction, after previous drilling of holes in the above sheet material for vacuum suction.